1. Field of the Invention
The invention relates to a radiation-sensitive resin composition, a method for forming a resist pattern, a polymer, and a compound.
2. Discussion of the Background
When producing a semiconductor device or the like, a resist film formed on a substrate is exposed via a mask pattern, and subjected to alkali development to form a fine resist pattern. Technology that utilizes a chemically-amplified resist that contains a photoacid generator that generates an acid upon irradiation as a resist film-forming resin composition has been known.
A further reduction in line width has been desired in the field of microfabrication, and liquid immersion lithography has been proposed to deal with such a demand. Liquid immersion lithography exposes a resist film via an immersion medium that has a refractive index higher than that of air and is provided between the lens of the exposure system and the resist film. Liquid immersion lithography makes it possible to achieve higher resolution even if a light source having the same wavelength is used (see Japanese Patent Application Publication (KOKAI) No. 11-176727, for example).
When using liquid immersion lithography, however, the composition that forms the resist film may be eluted into the immersion medium when the resist film has come in contact with the immersion medium. In this case, a deterioration in performance of the resist film, contamination of the exposure system (e.g., lens), or a decrease in resolution of the resist may occur. Moreover, since scan exposure is continuously performed at a high speed, droplets of the immersion medium tend to remain on the surface of the resist film, so that watermark defects may occur. Therefore, it is desirable that the surface of the resist film have high hydrophobicity.
Technology that incorporates a compound including a functional group that is hydrophobic during liquid immersion lithography, but becomes hydrophilic during alkali development, in a resist-forming resin composition has been developed (see Japanese Patent Application Publication (KOKAI) No. 2009-139909, for example). Japanese Patent Application Publication (KOKAI) No. 2009-139909 (see examples) discloses a compound that includes a benzene ring in which a fluoroacyl group is introduced into the side chain of an acrylic polymer or the like. In the compound disclosed in Japanese Patent Application Publication (KOKAI) No. 2009-139909, the fluorine atom is bonded to the carbon atom at the β position of the fluoroacyl group. The compound is unevenly distributed in the surface area of the resist film, so that the surface of the resist film exhibits hydrophobicity due to the fluorine atom during liquid immersion lithography, and exhibits hydrophilicity during alkali development due to a hydrophilic group produced via a reaction with the developer.